Conventional slam latches contain a spring-loaded latch bolt which is caught, for example, within a keeper (striker plate) when a door or panel is closed or slammed shut. As a door or panel closes, the latch bolt strikes against an inclined surface or keeper being angulated towards the direction of bolt reciprocation. This causes the latch bolt to retreat within the main mounting body holding the latch bolt and simultaneously compresses a spring. The door or panel continues to close until the latch bolt aligns with an opening contained within a surface (especially a planar surface) of the keeper, allowing the spring-loaded bolt to propel outwards until the latch bolt is contained within the keeper opening, thereby securing the door or panel. The doors or panels are predominantly constructed of steel and, in agricultural applications, must be strong enough to safely restrain any animals being handled.
In agricultural applications in particular, such doors or panels are regularly slammed shut at high speed, and one hundred percent operating retention rates are required to maintain operational safety. There is often no other means to stop the swinging door or panel from over rotating and moving past the locking position apart from the spring-loaded latch bolt propelling outwards and locating within the keeper opening. If the latch is used in an animal pen or crush, for example, then failure for the latch-bolt to locate within the keeper opening could injure an animal if the door or panel over-rotated, or a human if an animal pressed against a door or panel which was not successfully locked, thereby pushing the door or panel into the human or allowing the animal to escape.
Consequently, slam latch bolts are conventionally accommodated in a keeper opening that is larger than the latch bolt. Due to the speed and momentum of the door or panel as it is closed, such an oversize keeper opening is designed to allow sufficient time for the spring loaded latch bolt to propel outwards and locate within the opening and prevent the door or panel from travelling past the opening. However, this excessive gap may cause a rattle which causes additional stress to an animal.
Furthermore, operators may prefer to guide or push a door or panel shut, and often this is achieved by the operator holding or maintaining contact with the handle of the slam latch. In these circumstances, the operator's hand in particular may be subjected to high impact shock stress. This may cause operators to use the slam latch by closing the door or panel with less control (as to avoid shock stress the operator may not maintain contact with the door or panel), or it may discourage long term use. Furthermore, if the operator holds on to the handle, this may occasionally impede the spring-return function of the latch bolt.
Similar problems may arise with other types of latches, or in non-agricultural applications. In commercial offices, for example, a door may be designed to move open at certain times, and at other times the door may be designed to be secured closed. Such a door may be, for example, a sliding door, a folding door, a door that swings open in one direction, or a door that swings open in two directions (in which the door is closed in a central position). Such a door may be made of glass or timber and only need to retain lesser loads than in agricultural applications, for example. When it is desired to secure the door closed, the latch bolt is released and moves to engage with a keeper. However, when such a door is secured closed there conventionally exists an excessive gap between the latch bolt and the keeper which allows the door to rattle and thereby cause a public disturbance. The rattle may also convey that the door is not held as securely as it could be if there was no rattle.
It is an object of the present invention to provide a latch which minimises or overcomes at least one of the disadvantages of conventional latches described above, or to provide the public with a useful or commercial choice.